Boeing’s Starliner spacecraft landed on Earth early Saturday morning. Two test pilots remained in space until next year because NASA deemed their return too risky.

Starliner parachuted into space at White Sands Missile Range in New Mexico at 12:01 a.m. ET, six hours after leaving the International Space Station.

“I am extremely proud of the work our entire team put into this entire flight test, and we are pleased with the safe return of Starliner,” said Ken Bowersox, deputy director of the Space Operations Mission Directorate at NASA Headquarters in Washington, in a statement.

“Although it was necessary to return the spacecraft uncrewed, NASA and Boeing learned an incredible amount about Starliner in the most extreme environment possible,” he added. “NASA looks forward to our continued collaboration with the Boeing team to advance the certification of Starliner for crew rotation missions to the space station.”

Boeing Starliner departs space station and returns to Earth unmanned, leaving crew behind

The empty Boeing Starliner capsule lands at the White Sands Missile Range in New Mexico after undocking from the International Space Station. (NASA via AP)

This comes after Boeing’s long-delayed crew debut launched in June and a mission plagued by engine failures and helium leaks. The return of Butch Wilmore and Suni Williams was uncertain for months as engineers didn’t understand what was wrong with the spacecraft.

Boeing claimed after extensive testing that Starliner could bring the crew home safely, but NASA disagreed and instead hired SpaceX to fly them back to Earth. The SpaceX Starship won’t launch until later this month, so it will remain in space until February.

Wilmore and Williams were originally scheduled to fly back to Earth on the Starliner in mid-June, a week after launch. However, problems with the engines and a loss of helium occurred on the flight to the space station, so NASA concluded that it was too risky to bring them home on the Starliner.

After receiving new software updates, the fully automated capsule launched with the crew’s blue spacesuits and some old station equipment.

The Starliner’s crew demographics ended a series of delays and setbacks for the spacecraft.

After the space shuttles were retired more than a decade ago, NASA hired Boeing and SpaceX to provide orbital taxi service. But Boeing encountered many problems during its first uncrewed test flight in 2019, so it had to try again. The retry three years later revealed even more problems and the necessary repairs cost more than a billion dollars.

The unmanned Boeing Starliner capsule fires its engines as it lifts off from the International Space Station on Friday, September 6, 2024. (NASA via AP)

SpaceX’s Crew Ferry flight later this month will be the 10th the company has operated for NASA since 2020. The Dragon capsule will launch on the six-month expedition with just two astronauts, as two seats are needed to bring Wilmore and Williams back home.

The Starliner’s propulsion system began leaking helium before launch from Cape Canaveral in Florida in early June. The leak was small and presumably isolated, but four more were discovered after launch. Five engines subsequently failed, and although four of them were recovered, the problems raised concerns at NASA that further malfunctions could cause problems during the capsule’s descent from orbit.

Boeing conducted numerous engine tests in space and on Earth over the summer and was confident that its spacecraft could return the astronauts safely. However, NASA remained skeptical about the engine problems and contracted SpaceX to carry out the return.

After undocking, flight controllers conducted more test firings of the capsule’s engines, but one failed to fire. Engineers believe that with more frequent firings, the engines get hotter, causing the protective seals to swell and impede fuel flow. None of the parts can be examined because the section holding the engines was ejected just before reentry.

NASA astronaut says Starliner crew will likely change their training routine during their extended ISS stay

The unmanned Boeing Starliner capsule will undock from the International Space Station on Friday, September 6, 2024. (NASA via AP)

Starliner will be returned to NASA’s Kennedy Space Center.

“I want to commend the work of the Starliner teams to ensure a successful and safe undocking, deorbiting, reentry and landing,” said Mark Nappi, vice president and program manager of Boeing’s Commercial Crew Program, in a statement. “We will review the data and determine next steps for the program.”

Steve Stich, NASA’s commercial crew program manager, said earlier this week that the space agency wants to continue to use two competing U.S. companies to transport astronauts into space. NASA hopes SpaceX and Boeing can take turns transporting crews until the space station is abandoned in 2030 ahead of its fiery reentry.

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“We are pleased that Starliner arrived home safely. This was an important test flight for NASA to prepare for future missions in the Starliner system,” Steve Stich, manager of NASA’s Commercial Crew Program, said in a statement after Starliner returned to Earth. “We gained a lot of valuable knowledge that will enable our long-term success. I want to thank the entire team for their hard work and dedication over the past three months.”

The Associated Press contributed to this report.